If I want to start timer upon pressing Start on title screen, what delay should I set in my timer?

-2.70. I am very late to reply, but this is generally how long it takes. This isn't 100% accurate because of framerule stuff, better to start the timer when you select a mode in your Super Mario Bros./Duck Hunt cartridge, which should be -3.27 if you want to start ASAP. Add -0.35 per framerule you want to start later than that.

You want to start the timer with a -2.63 on it if you are going from power on, and if you are starting the game on the first possible framerule. Add -0.35 to the timer for each later frame rule you start on.